The tennis world is gearing up for the ATP World Tour Finals, where 8 of the best male players will vie for the final major title of 2016. One of the things that could be decisive in who advances to the semifinals is the pressure of the return. Here, when I refer to return pressure, I am thinking of the kind of player who jumps on the serve and makes an attacking shot that gives the server little time to react. We all have a sense that some players do a better job at putting the pressure on even when in the defensive role, but we rarely see numbers that can help tell us who these players are.

In this post, I take a stab at measuring “return pressure” as part of the ongoing AO Leaderboard series brought to you by Tennis Australia’s Game Insight Group. Using player and ball tracking data from the 2014 to 2016 Australian Open, we define the pressure of the return by how much time the returner gives the server to react to their first shot. The less time the server has to prepare for his or her next shot (serve + 1), the more pressure the server feels.

The time it takes the return shot to reach the server is determined by the speed of the returner’s shot and where each player is positioned. A returner can hit the ball hard but if he is 5 feet behind the baseline (Ahem… Nadal), it doesn’t create the same kind of pressure as a ball moving at the same speed that is hit from 1 foot inside the baseline.

Another factor to consider is the speed of the server’s ball. If a player has seen slower serves, their typical return speed might look more impressive than it should or vice versa. If we want to isolate the role of the return apart from serve, we want to compare players as if they had returned the same mix of serves.

The return pressure stats below attempt to account for these factors (service speed and player positioning) by looking at a player’s estimated return speed for an average serve (that is, a serve traveling at the average speed for their tour), including first and second serves. This rate is multiplied by the player’s typical distance from the baseline. Putting this all together, the return pressure metric is expressed as the expected seconds it takes for the returner’s ball to reach the net when receiving a “typical” serve.

On the men’s side, we see several of the 8 competitors in the tour finals at the top of the return pressure rankings. Novak Djokovic and Kei Nishikori are top among them, each having an expected 0.43 seconds for their returns to cross the net on an average serve. Other players with the most return pressure include players with some of the most aggressive playing styles in the game, like Lukas Rosol and Tomas Berdych, as well as players with big groundstrokes, like Milos Raonic and Juan Martin Del Potro. (Note that some of the players at the very top have smaller sample sizes on return than others, which is reflected by the size of the points on the plot, and should be interpreted with more caution.)

On the other end of the spectrum, Rafael Nadal is one of the players with the least return pressure among the group. This shouldn’t be a surprise because Nadal is known to position himself far behind the baseline on most serves. More surprising is to see Gael Monfils, one of the players who will compete at the O2, at the bottom of the return pressure rankings. This could also be due to his positioning or suggest that an attacking stance is not as consistent for Monfils than other players. It will be interesting to look for those patterns in the coming days.

For the WTA, return pressure appears to align much more closely with success on tour. Some of female players we see as taking away the most time from the server on the serve+1 shot include Petra Kvitova, Garbine Muguruza, and the Williams sisters. Other players who cluster toward the top are known for their aggressive style, like Victoria Azarenka and Madison Keys. Player on the rise, Karolina Pliskova, and gold medalist, Monica Puig, are also in the mix of players with return pressures of 0.43 seconds or less.

Toward the bottom of the list are some of the counter-punching players like Caroline Wozniacki and Saisai Zheng. World No. 1 Angelique Kerber, despite a move to a more aggressive style of play, still remains on the defensive side according to the return pressure metric. We also see that attackers Naomi Osaka and Dasha Gavrilova might have room to assert more aggressiveness on the return.

An intriguing observation when we contrast the men’s and women’s return pressure at the AO is that top women actually exert more pressure than the comparable top men. In other words, WTA returners tend to take away more time from the server’s second shot than ATP returners. This could be due to the fact that WTA players tend to create less pressure on serve than male players, giving the returner greater ability to take a ball early and further inside the baseline. So, while the power and speed of the men’s and women’s games may not be equal, in some respects, the women have the upperhand.